Method of manufacturing a hermetically sealed mat switch

ABSTRACT

AN ELECTRICAL MAT SWITCH COMPRISES A FULLY SENSITIVE CONTACT PLATE SUBASSEMBLY HERMETICALLY ENCLOSED BY PREFORMED BASE AND COVER LAYERS WHICH EXTEND OUTWARDLY BEYOND THE PERIPHERY OF THE SUBASSEMBLY AND PORTIONS OF ACCURATELY DIMENSIONED LOCATOR STRIPS WHICH ABUT THE EDGES OF THE SUBASSEMBLY AND FACILITATE THE PERIPHERAL HEAT SEALING ENCLOSURE THEREOF.

June 1, 1971 P, v SHAVER 3,581,391 I METHOD OF MANUFACTURING A HERMETICALLY SEALED MAT SWITCH Filed out. v, 195e 2 sheets-sheet z Y United States Patent O 3,581,391 METHOD F MANUFACTURING A HERMETI- CALLY SEALED MAT SWITCH Paul V. Shaver, Wallingford, Conn., assigner to The Stanley Works, New Britain, Conn. Filed Get. 7, 1968, Ser. No. 765,347 Int. Cl. H01h 11/00 U.S. Cl. 29--622 7 Claims ABSTRACT 0F THE DISCLGSURE The present invention relates to electric mat switches for use with automatic door operating systems and the like. More particularly, it is directed to both a new and improved mat switch normally positioned at the ingress and/or egress portions of a door opening for actuation by pedestrian traic and a new and improved process for manufacturing a hermetically sealed mat switch.

An object of the present invention is to provide a mat switch of the type described which is made from preformed components and is hermetically sealed about its entire periphery in a rapid, facile and economical manner without the necessity of using heavy molds completely encasing the entire switch.

Another object of the present invention is to provide a new and improved method for manufacturing mat switches of the type described which enables the useof substantially the same basic equipment for the manufacture of mat switches in a variety of sizes and shapes.

A further object of the present invention is to provide a new and improved method for manufacturing a hermetically sealed mat switch which utilizes preformed and preassembled components and necessitates the application of heat and pressure only on the peripheral portions of the mat switch thereby obviating potential damage to the spaced contact plates of the switch.

Still another object of the present invention is to provide a new and improved method of the type described which provides for accurate aligned assembly of preformed parts and subsequent heat sealing of only the peripheral portions of the mat switch via dielectric heating.

A still further object of the present invention is to provide a new and improved hermetically sealed electric mat switch of the type described which is produced from preformed components and is heat sealed about its periphery so as to exclude moisture and foreign matter which might interfere with the normal operation of the switch, the preformed components permitting the use of decorative materials on exposed surfaces of the mat without necessitating the use of bulky and expensive decorative molds.

An additional object of the present invention is to provide a hermetically sealed mat switch having uniform and full sensitivity over its entire contact area and being heat sealed about its periphery at a controlled and accurately spaced distance from the contact plates of the switch.

A further object of the present invention is to provide a new and improved method for manufacturing hermetically sealed electric mat switches of the type described which employs a heat sealable locator strip about the periphery of the contact plates for accurately positioning and heat sealing the assembly While maintaining a correct peripheral height and acting as an insulating barrier for the contact plates of the mat switch.

Other objects will be in part obvious and in part pointed out more in detail hereinafter.

The invention accordingly consists in the features of construction, combination of elements and arrangement of parts which will be exemplified in the construction hereafter set forth and the scope of the application which Will be indicated in the appended claims.

In the drawings:

FIG. 1 is a diagrammatic and schematic view illustrat lng the various steps in the improved manufacturing process of the present invention; and

FIG. 2 is an enlarged sectional view illustrating the peripheral or edge structure of the mat switch as it is heat sealed and trimmed by the dielectric heating device used in accordance with the present invention.

Referring generally to the iiow diagram of FIG. l wherein like reference numerals indicate like parts, the initial step in the process of the present invention is the formation of a contact plate subassembly, generally designated by the numeral 10, which preferably will have full and substantially uniform sensitivity over its entire area, that is, contact between the plates thereof can be eectuated by applying pressure to any area of the top plate. The contact plate or Switch subassembly r is sandwiched beween a base layer 12 and cover layer 14 of heat sealable material which overhangs or extends beyond the edges of the subassembly on all four sides to facilitate the eventual hermetic enclosure of the mat. Accurately dimensioned locating strips 16 are then inserted between the top and bottom layers in such a manner that they abut the edges of the contact plate subassembly 10 about its entire periphery. The unsealed mat switch assembly thus formed is accurately positioned against guide members 18 on a fiat plate-like electrode 20 of the sealer, generally designated 22, the electrode 20 being rollably carried by a supporting table 214 of the sealer 22 for movement between an assembly station 26 and a sealing station 28. Since the electrode 20 can be readily and accurately located relative to the top power unit 30 of the sealer by the detent stops 34 and the locating strips 16 are accurately dimensioned, the contact plate subassembly 10 is thereby accurately positioned relative to unit 30 so that heating will be effectuated only within an area spaced outwardly of the periphery of the contact plate subassembly 10i. The sealer 22 rapidly causes a hermetic heat seal about the periphery of the assembly and is also adapted to trim the excess peripheral portion of the mat after the heat sealing operation has been completed.

Referring now to the drawings in greater detail, the initial step of the process, as mentioned hereinbefore, envisions the formation of a contact plate subassembly 10 for the mat switch. In the embodiment illustrated, the subassembly includes a pair of flat, generally rectangular, sheet metal contact plates 36, 38 of substantially the same planar dimensions superimposed in overlying registry and enclosing both a plurality of insulating dot spacers 40 and a continuous gasket 42 which separates the plates about the entire peripheral portions thereof. As shown the corners of plates 36, 38 have `been chamfered at 32 to avoid accidental bending or other damage thereto which might interfere with the reliable operation of the mat switch. The dot spacers 40 and gasket 42 are both insulators and can be formed from the same or different rnaterials. For example, commercially satisfactory results have been obtained from subassemblies using preformed nitrile rubber spacers and a paper gasket. Both the spacers and gasket are preferably bonded or otherwise secured to at least one of the electrically conductive plates 36, 38 to assure accurate positioning thereof and therefore full sensitivity of the pressure responsive switch. Thus, the top plate 38 of the subassembly which preferably has a thickness of about 0.0105 inch is held out of contact with the more rigid bottom plate 36 principally by the rubber spacers 40* which are suitably dispersed in an ordered fashion to permit contact between the plates when pressure is applied to any area of the top contact plate such as by the weight of a pedestrian. As mentioned, the bottom plate 36 is preferably more rigid and may beneficially exhibit a thickness three times that of the top plate 36. For example, a bottom plate having a thickness of 0.031 inch has been employed with good success.

Suitable electrical connections 44 are also aflixed to the respective plates and the entire subassembly is peripherally enclosed and secured by a suitable means such as a strip of insulating tape 46 which extends around the entire subassembly thereby initially sealing the interior thereof against moisture or foreign matter which might interfere with its operation. Advantageously, the production of the subassembly can be accomplished at a time and place remote from the other operations of the process and well prior to the hermetic sealing and trimming of the mat assembly. Thus, the contact plate subassembly might be stored for a length of time prior to being formed into the final product.

As indicated, the preformed contact plate subassembly 10 is interposed `between the base and cover layers 12, 14 of the mat. These layers can easily be fed from their respective storage rolls 52, 54 and cut to appropriate lengths for enclosing the subassembly. The base and cover layers 12, 14 are both preferably formed from heat sealable sheet materials such as vinyl or other suitable thermoplastics. The layers are of substantially the same width and, when cut, extend beyond all the edges of the subassembly sandwiched therebetween, the latter being of smaller planar dimensions in both directions. Although the base and cover layers are of substantially equal thickness, the cover layer 14 may be provided with a serrated top surface 56, as shown, while the base layer 12 is a smooth flat member which will not be exposed during use. Additionally, or alternatively, the cover layer 14 may be a composite member having a color controlled emblem or other decorative material visible thereon.

In accordance with the present invention it has been found advantageous to adhesively secure the base and cover layers to the subassembly 10. Thus, an adhesive 48 may conveniently be applied to both surfaces of the subassembly 10 and/or to the interior surfaces of the base and cover layers immediately prior to assembly. Accordingly, the adhesive will reduce excessive movement of the subassembly 10 relative to the base and cover layers prior to the heat sealing operation. However, it is an advantage of the present invention that the subassembly need not be accurately and precisely positioned between the layers, it being sufiicient merely to place the subassembly 10 at approximately the center of the enclosing layers.

The subassembly 10 and its enclosing top and bottom layers 12, 14 are next fitted with the accurately dimensioned locator strips 16. Although this operation may be performed at a location remote from the sealer 22, there is au obvious advantage in assembling the strips 16 while the adhered sandwich structure is positioned on the electrode 20 at the assembly station 26. This is particularly true since the subsequent mat sealing operation requires relatively accurate positioning of the unsealed assembly and the locator strips are preferably left unadhered so as not to interfere with the heat sealing operation. The strips 16 are of substantially the same thickness or height as the subassembly 10, e.g. 0.117 inch, and are precisely formed to a known and accurately dimensioned width so that the alignment of the entire assembly can be effectuated through contact of the locator strips with the guide members 18 along at least two sides of the unsealed assembly. In the preferred embodiment, the circumscribing action of the locator strips 16 is interrupted at the location of the protruding electrical leads 44 While the strips themselves are contoured or recessed at to accommodate the connecting portions of the electrical lead wires. The strips on the electrical lead side of the assembly are typically of a width on the order of 0.375 inch while the strips around the remainder of the subassembly 10` are substantially wider, e.g. about 1.31 inches. Consequently the strips on the electrical lead side of the unsealed assembly do not extend outwardly beyond the edges of the layers 12, 14 in the same manner as the wider strips located on the remaining three sides of the mat. 1n fact, the width of the strips on the electrical lead side is approximately the same as the distance between the subassembly 10 and the inner edge of the heat seal subsequently formed so that the seal along that side is effected between only the layers 12, 14. Advantageously this thinner edge along one side of the mat will then better accommodate the threshold molding therealong. Since the strips physically abut all of the taped sides 58 of the subassembly 10` and in turn are in intimate contact with the guide members 18 along two sides of the unsealed mat, they provide for accurate alignment of the subassembly relative to the top power unit :30 during the heat sealing operation. The strips 16 are made of softenable plastic such as heat sealable vinyls or other thermoplastics compatible with the cover and base layers and those portions of the strips located beneath the top electrode will be heated to a pliable condition during the sealing operation. As best shown in FIG. l the locator strips 16 are elongated, flat, generally rectangular members but mayinclude triangular corner fillers 60 of the same material to compensate for and fill the voids created by the chamfered corners 32 provided on the subassembly 10 for avoiding accidental bending of the subassembly at those vulnerable locations.

The dielectric sealer 22 includes a mat supporting table 24 having an assembly station 26 and a sealing station 28. The table 24 includes a fiat, elongated, generally rectangular top surface 62 provided :with fixed elongated side rails 64 upstanding from and extending along the longitudinal edges thereof for positionably regulating the travel of the fiat lower electrode 20 as it moves between the assembly and sealing stations. The electrode 20 which takes the form of a shuttle lling the entire width of the track defined by the parallel rails 64, is assisted in its movement between the stations by a plurality of rollers 66 mounted within and protruding slightly above the top surface 62 at regularly spaced locations along the table 24. As shown in FIG. 2, the rollers 66 may be spring loaded so that as the unit 30 presses against the mat assembly for effecting the sealing of the mat, the bottom electrode 20 will depress the rollers 66 and come into firm supporting contact with the -fiat top surface 62 of the table 24. The shuttle electrode 20 is additionally provided with four pairs of upstanding posts 68 located generally at the four corners of the electrode 20 for mounting the wheel support blocks 70 of the shuttle. Springs 72 mounted on the lposts 68 act against the blocks 70` and retaining washers 74 to bias the shuttle into a slightly elevated position above the top surface 62 of the table 24 while at the same time permitting the depressable positioning thereof at the sealing station 28. Each corner block 70 mounts a wheel 76 positioned to roll along the top of side tracks 64. Additionally, the blocks on one end ofthe shuttle mount a second outwardly spaced wheel 78 adapted to engage the detent stop 34 for fixedly positioning the shuttle at the sealing station 28. The wheel 78 also serves to hold the shuttle in the assembly station 26 through cooperative engagement with the detent stop 80 affixed to the outside of track 64 at that station.

The shuttle electrode, after assembling and positioning the unsealed mat assembly thereon, is moved out of the assembly station 26 and into the heat sealing station 28 by merely rolling it along the table 24 on the rollers 66 and rails 64. The electrode and therefore the unsealed assembly is locked into position at the sealing station beneath the power unit 30 of the sealer 22 through the engagement of the wheels 78 with the detent stop 34 and is ready for the sealingand trimming operation. The dielectric heating unit 30 includes a power operated die 82 movable toward and away from the lower electrode 20 to which it is electrically connected by means not shown. The die 82 is provided with a depending narrow top electrode 84 which extends around the perimeter thereof with a single interruption 86 at the position overlying the electrical leads. Because the sealing operation at the lead cord area requires a different technique to accurately locate and bond the leads such as the use of balance dielectric heating from both electrodes, it is hermetically sealed independently of the remainder of the mat after the main sealing station by modifying the sealing apparatus ilheating the leads would shield the area directly below them and effectively oat to the surface of the vinyl. This sealing is usually carried out after the main sealing operation and can be eHected on a separate sealer or at the sealing station by modifying the sealing apparatus illustrated. In accordance with the preferred embodiment of the invention the heat sealing die 82 is brought into contact with the unsealed mat switch assembly in such a manner that only the narrow peripheral top electrode 84 contacts the top surface 56 of the cover layer and applies a slight pressure thereto. The die 82 readily pushes the electrode 20 downwardly against the upward bias acting on rollers `66 to firmly seat the electrode 20 against the flat top surface :6-2 of the table 24. In this way there is provided not only a solid and fixed support for the mat during sealing but a more equal distribution o-f dielectric energy around the periphery of the carpet assembly. In this connection, suitable adjustments are made along the lead wire edge of the assembly to compensate for the lack of a spacer member across the full extent of the seal.

As best shown in FIG. 2, the electrode is dimensioned so as to contact the cover layer 14 outwardly of the contact plate subassembly 10, for example by a distance of approximately 0.3-0.4 inch, and to provide a sealed edge having a width of approximately 0.25 inch. Although the sealing time will vary to accommodate both the voltage fluctuation and the thickness of the mat at the portion being sealed, the time required for sealing is generally only about 7 to 13 seconds. According, it will be appreciated that the thickness of the sealed edge is controlled by a combination of the initial thickness of the material, the pressure applied by the die, and the degree and length of heating which takes place. The dielectric heating coupled with the pressure from the die rapidly renders the heat sealable material within the base and cover layers as well as within the locating spacer sufficiently uid to form a water impermeable bond or seal. Advantageously, use of a dielectric heating technique localizes and confines the heating to the edge of the mat outwardly from the electrical components of the subassembly, while the locator strip additionally maintains the desired peripheral height on the mat and acts as an insulating barrier for the contact plates of that mat switch.

As shown in FIG. 2 an edge trimming knife 94 is carried by the top power unit 30 and is kept out of contact with the mat switch during the heating cycle of the sealing operation. The knife 94 depends from a supporting block 96 and operates reciprocally along the side of the electrode 84 and spporting die 82 to trim the mat in guillotine fashion. The knife supporting block 96 carried by the die 82 is maintained in overlying spaced relationship thereto by compression springs 98 until the heating operation is complete. At that time an independent power source (not shown) is actuated to move the block 96 and knife 94 downwardly against the bias of springs 98 to a point just short of the lower electrode 20 causing the knife to substantially sever the mat at the outward edge of the heat seal 'and permit subsequent removal of the excess material. The entire top unit 30 is retained in its lowered position for a short cooling period, e.g. about 12 seconds to hold in position the owably pliable material at the seal area and advantageously serve as a heat sink to rapidly draw away heat and reduce the time required for cooling. The unit 30 is then raised and the mat removed for nal heat `sealing at the point where the electrical leads 44 protrude from the mat thereby assuring a completely watertight and hermetic seal for the mat switch.

As can be seen from the foregoing detailed description the present invention provides a novel, unique and substantially' improved mat switch assembly and method for its manufacture. The mat switch is made from preformed components which can be easily and quickly assembled from stock materials in a rapid, facile and economical manner and is heat sealed along its entire edge without the necessity of bulky and cumbersome molding equipment. The method and assembly employ a precisely dimensioned locator strip for accurately positioning the electrical components of the mat switch prior to and during the sealing operation. The locator strip constitutes part of the accurate edge seal which excludes moisture and other foreign matter from interfering with the normal operation of the switch. Additionally, the hermetically sealed mat switch is provided with uniform and full sensitivity throughout its entire contact area and readily permits the use of decorative materials on the exposed surface thereof while the improved method of manufacture obviates any adverse elfect which might result from subjecting the contact plates of the switch to a heating operation.

As will be apparent to persons skilled in the art, various modications and adaptations of the structure abovedescribed will become readily apparent without departure from the spirit and scope of the invention, the scope of which is defined in the appended claims.

I claim:

1. A method of manufacturing a hermetically sealed electric mat for sensing the presence of an object thereon, comprising the steps of providing an unsealed mat assembly comprising a control plate subassembly sandwiched between base and cover layers; encircling the control plate subassembly with a locating strip positioned between the base and cover layers; accurately positioning the unsealed assembly relative to a dielectric heating device by means of the locating strip; and subsequently dielectrically heating the unsealed assembly outwardly of the control plate subassembly to form a peripheral heat seal spaced from the subassembly.

2. The method of claim 1 wherein the locating strip is of a controlled width having an inner edge abutting the control plate subassembly and the dielectric heating is effected through a portion of the strip outwardly of the inner edge.

3. The method of claim 1 wherein the locating strip is of a controlled width and the unsealed assembly is accurately positioned relative to a dielectric heating device by abutting the outer edge of the strip against a portion of the device fixed relative to the heater during the heatlng operation.

4. The method of claim 1 wherein at least a portion of the assembly extends outwardly of the heat seal and the assembly is subsequently trimmed adjacent the outer edge of the heat seal by cutting away said outwardly extending portion.

5. The method of claim 1 wherein the subassembly includes a pair of spaced Contact plates and a peripheral seal for the spaced contact plates thereby providing an internal secondary seal for the hermetically heat sealed assembly.

6. The method of claim 1 wherein the step of providing an unsealed assembly includes the steps of applying a plurality of spacers to one side of a lirst generally flat electrically conductive plate; placing a second flat electrically conductive plate on said spacers in parallel overlying relationship to the first plate; securing the first and second plates together to form the control plate subassembly; and wherein the subassembly is adhered between base and cover layers of greater planar dimensions than the subassembly.

7. The method of claim 1 wherein the step of providing an unsealed subassembly includes the steps of applying a plurality of spacers to a rst generally flat conductive plate; placing a second conductive plate of substantially the same planar dimensions on said spacers in parallel overlying relationship to the irst plate to form lthe control plate subassembly; wherein the base and cover layers are of greater planar dimensions than the subassembly; and wherein the locating strip is of a controlled, substantially uniform width with at least a portion of the strip resting betweeuthe base layer and the cover layer and having an inner edge abutting the subassembly; and the base layer, cover layer and locating strip are dielectrically heated outwardly of said inner edge to peripherally heat seal the strip to both the base layer and the cover layer.

References Cited UNITED STATES PATENTS 2,583,813 1/1952 Burke 29-622X 3,056,005 9/1962 Larson 200-86 3,102,186 8/1963 Owers 156-273X 3,323,197 6/ 1967 Millard 29--622 FRANK T. YOST, Primary Examiner U.S. Cl. X.R. 200-86 

